Fluid pump

ABSTRACT

A fluid pump includes a drive shaft driven by power from an engine, a rotor adapted to be provided at a housing and rotating unitarily with the drive shaft, a driving wheel which is provided separately from the drive shaft and to which the power from the engine is always transmitted when the engine is running, a driven wheel transmitting the power from the engine to the drive shaft upon being in contact with the driving wheel, and a displacement mechanism causing the driving wheel and the driven wheel to be out of contact from each other by moving at least one of the driving wheel and the driven wheel.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is based on and claims priority under 35 U.S.C. §119 toJapanese Patent Application 2010-240587, filed on Oct. 27, 2010 andJapanese Patent Application 2010-221650, filed on Sep. 30, 2010, theentire contents of which are incorporated herein by reference.

TECHNICAL FIELD

This disclosure relates to a fluid pump.

BACKGROUND DISCUSSION

According to a known fluid pump disclosed in JP2008-169763A, drivingpower of an engine is transmitted by means of an accessory driving beltwound around a driving pulley. Thus, as the driving pulley rotates, arotary shaft rotates. When the rotary shaft rotates, an impeller rotatesunitarily with the rotary shaft, thereby circulating a cooling waterthrough an engine cooling system.

According to a variable displacement fluid pump disclosed inJP2009-293578A, effective heights of vanes are changed by means of amovement of a movable member. According to the variable displacementfluid pump, the effective heights of the vanes are changed on the basisof a change in a volume of a thermo wax which is caused by a heattransmission, thereby varying a discharge amount of the variabledisplacement fluid pump.

However, the fluid pump disclosed in JP2008-169763A always circulatesthe cooling water when the engine is running. This may restrict areduction in a warm-up time of the engine because the cooling water iscirculated even during a start-up of the engine.

The variable displacement fluid pump disclosed in JP2009-293578A alwaysoperates even when the effective heights of the vanes are at the minimumheight, thereby generating a driving torque. This may result in a wastedconsumption of power.

A need thus exists for a fluid pump which is not susceptible to thedrawback mentioned above.

SUMMARY

According to an aspect of this disclosure, a fluid pump includes a driveshaft driven by power from an engine, a rotor adapted to be provided ata housing and rotating unitarily with the drive shaft, a driving wheelwhich is provided separately from the drive shaft and to which the powerfrom the engine is always transmitted when the engine is running, adriven wheel transmitting the power from the engine to the drive shaftupon being in contact with the driving wheel, and a displacementmechanism causing the driving wheel and the driven wheel to be out ofcontact from each other by moving at least one of the driving wheel andthe driven wheel.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing and additional features and characteristics of thisdisclosure will become more apparent from the following detaileddescription considered with the reference to the accompanying drawings,wherein:

FIG. 1 is a cross-sectional view of a water pump related to a firstembodiment disclosed here;

FIG. 2 is a cross-sectional view of an actuator related to the firstembodiment disclosed here;

FIG. 3 is a diagram explaining a state in which a driving pulley and adriven pulley related to the embodiments disclosed here are in contactwith each other;

FIG. 4 is a diagram explaining a state in which the driving pulley andthe driven pulley are out of contact from each other;

FIG. 5A is a diagram explaining an example in which a pulley ratiobetween the driving pulley and the driven pulley whose outercircumferential surface is in contact with an inner circumferentialsurface of the driving pulley is changed, where a diameter of the drivenpulley is φB;

FIG. 5B is a diagram explaining an example in which the pulley ratiobetween the driving pulley and the driven pulley whose outercircumferential surface is in contact with the inner circumferentialsurface of the driving pulley is changed, where the diameter of thedriven pulley is φB/2;

FIG. 6A is a diagram explaining an example in which the pulley ratiobetween the driving pulley and the driven pulley whose outercircumferential surface is in contact with an outer circumferentialsurface of the driving pulley is changed, where the diameter of thedriven pulley is φD;

FIG. 6B is a diagram explaining an example in which the pulley ratiobetween the driving pulley and the driven pulley whose outercircumferential surface is in contact with the outer circumferentialsurface of the driving pulley is changed, where the diameter of thedriven pulley is φD/2;

FIG. 7 is a cross-sectional view of a water pump related to a secondembodiment disclosed here;

FIG. 8 is a cross-sectional view of a water pump related to a thirdembodiment disclosed here; and

FIG. 9 is a cross-sectional view of a water pump related to a fourthembodiment disclosed here.

DETAILED DESCRIPTION

Embodiments of this disclosure will be explained with reference to theattached drawings.

As shown in FIG. 1, a water pump 1 (a fluid pump) related to a firstembodiment of this disclosure includes a pump body 11 (a housing) whichis made by casting or other methods and is adapted to be fixedly mountedon an engine block 12 (the housing) by means of a bolt. A bearing shaft10 (a drive shaft) is supported at the pump body 11 via a bearing 13 ina manner that the bearing shaft 10 rotates about a rotation axis thereofrelative to the pump body 11.

An impeller 20 (a rotor) is housed in a pump housing 21 formed betweenthe pump body 11 and the engine block 12, and is fixedly coupled to oneend of the bearing shaft 10 by means of press-fitting or other methods.A mechanical seal 14 having an annular shape is provided on an outercircumferential surface of the bearing shaft 10 so as to be positionedbetween the impeller 20 and the bearing 13 in an axial direction of thebearing shaft 10 in order to restrict coolant water from intruding intothe pump body 11. A driven pulley 40 (a driven wheel) is fixedly coupledto the other end of the bearing shaft 10. A friction material 41 isapplied to an outer circumferential surface of the driven pulley 40.

A driving pulley 30 (a driving wheel) is positioned so that an innercircumferential surface of the driving pulley 30 is contactable with anouter circumferential surface of the driven pulley 40. That is, thedriven pulley 40 is provided at an inside of a hollow portion of thedriving pulley 30. Power from an engine is transmitted to the drivingpulley 30 via a belt 31 (a power transmitting member) wound around anouter circumferential surface of the driving pulley 30. The drivingpulley 30 is fixedly coupled to one end of a driving pulley bearingshaft 32 so as to rotate with the driving pulley bearing shaft 32. Afriction material 33 is applied to the inner circumferential surface ofthe driving pulley 30 so that a friction force is generated between thefriction material 33 and the friction material 41 that is applied to theouter circumferential surface of the driven pulley 40 when the drivingpulley 30 and the driven pulley 40 are in contact with each other. Thepower from the engine, that is, the power generated by the engine istransmitted from the driving pulley 30 to the driven pulley 40 by meansof the friction force. An actuator 50 (a displacement mechanism) iscoupled to the other end of the drive pulley bearing shaft 32.

As shown in FIG. 2, the actuator 50 includes a slide 51 supporting thedriving pulley bearing shaft 32 via a drive pulley bearing 53 in amanner that the drive pulley bearing shaft 32 rotates about a rotationaxis thereof relative to the slide 51. A slide guide 52 is provided atthe slide 51 so as to cover the slide 51 having a piston-like structure.The slide guide 52 is configured in a manner that the slide 51 ismovable relative to the slide guide 52 in a perpendicular direction 62that is perpendicular relative to a direction of a resultant force 61 ofa tensile force 60 a (a force) and a tensile force 60 b (the force) bothof which act on the belt 31 that is wound around the outercircumferential surface of the driving pulley 30. A spring 54 (aresilient member) for causing the driving pulley 30 to come in contactwith the driven pulley 40 by means of a resilient force is providedbetween the slide 51 and the slide guide 52 in the perpendiculardirection 62. A closed chamber 55 is provided between the slide 51 andthe slide guide 52, where the spring 54 is provided. The closed chamber55 is provided in a manner that a pressure therein is controllable. Whena negative pressure (a gas pressure) is applied to the closed chamber 55and then the pressure inside the closed chamber 55 decreases, the slide51 moves in the perpendicular direction 62 until reaching a position inwhich the negative pressure of the closed chamber 55 is balanced out bythe resilient force of the spring 54, that is, the slide 51 moves in theperpendicular direction 62 until a movement of the slide 51 caused bythe negative pressure is balanced out by the movement of the slide 51caused by the spring 54. As the slide 51 moves, the driven pulleybearing shaft 32 supported by the slide 51 also moves in theperpendicular direction 62, and thus a state where the driving pulley 30and the driven pulley 40 are out of contact from each other isestablished.

Next, an operation of the water pump 1 of this disclosure will beexplained.

In FIG. 3, the driving pulley 30 and the driven pulley 40 are in contactwith each other, that is, the driving pulley 30 and the driven pulley 40are connected with each other so that a power transmission is achievedtherebetween. The belt 31 wound around a crank pulley and on the drivingpulley 30 rotates the driving pulley 30, and thus the power from theengine is transmitted to the driving pulley 30. The driving pulley 30 iscaused to come in contact with the driven pulley 40 by the resilientforce of the spring 54 provided in the actuator 50. When the drivingpulley 30 is in contact with the driven pulley 40, the friction force isgenerated between the friction material 33 of the driving pulley 30 andthe friction material 41 of the driven pulley 40, and thus the powerfrom the engine is transmitted from the driving pulley 30 to the drivenpulley 40. That is, the driving pulley 30 and the driven pulley 40 areconfigured to be unitarily rotatable with each other. As the drivenpulley 40 rotates, a rotation of the driven pulley 40 is transmitted tothe impeller 20 via the bearing shaft 10 and consequently, the powerfrom the engine is transmitted to the impeller 20. As the impeller 20rotates, the coolant water contained in the pump housing 21 isdischarged via an outlet of the pump 1 and circulated through theengine.

In FIG. 4, the driving pulley 30 and the driven pulley 40 are out ofcontact from each other, that is, the driving pulley 30 and the drivenpulley 40 are disconnected from each other so that no power transmissionis achieved therebetween. When the negative pressure is applied to theclosed chamber 55 of the actuator 50, a force attracting the slide 51(an attracting force) moves the slide 51 in the perpendicular direction62 against the resilient force of the spring 54, and thus the drivingpulley 30 comes out of contact from the driven pulley 40. When the outercircumferential surface of the driven pulley 40 is out of contact fromthe inner circumferential surface of the drive pulley 30, no frictionforce is generated between the friction material 33 of the drivingpulley 30 and the friction material 41 of the driven pulley 40, and thusno power is transmitted from the driving pulley 30 to the driven pulley40. Accordingly, an operation of the impeller 20 in the pump housing 21remains stopped, which stops the coolant water from circulating throughthe engine.

According to the water pump 1 related to the first embodiment, theactuator 50 causes the impeller 20 to stop rotating when the enginestarts up by moving the drive pulley 30 so that the drive pulley 30comes out of contact from the driven pulley 40. Thus, an overcooling ofthe engine is restricted and a warm-up time of the engine is reduced.

No power is transmitted from the engine to the impeller 20 when theimpeller 20 stops rotating, thereby restricting a wasted consumption ofthe power.

Because the actuator 50 moves the drive pulley 30 in the perpendiculardirection 62 relative to the direction of the resultant force 61 of thetensile force 60 a and the tensile force 60 b, the resultant force 61 ofpressing forces that are caused by the belt 31 and are applied to theactuator 50 is less likely to interfere with the movement of the slide51. Thus, a force of the actuator 50 for moving the driving pulley 30 isrestricted from acting against the resultant force 61 of the pressingforces that are caused by the belt 31 and are applied to the actuator50. Accordingly, the actuator 50 needs to supply only sufficient forceto move the driving pulley 30, and as a result, the actuator 50 having asmall size is provided.

The actuator 50 causes the driving pulley 30 to come in contact with thedriven pulley 40 by means of the resilient force of the spring 54 whenno negative pressure is applied to the closed chamber 55, and thus theimpeller 20 rotates. Therefore, even in case that the pressure of theclosed chamber 55 is out of control for any cause, the driving pulley 30and the driven pulley 40 remain in contact with each other according toa normally-closed principle, that is, a path of power transmission isclosed, and thus the impeller 20 rotates, which provides a fail-safestructure. The fail-safe structure refers to a structure in which thedriving pulley 30 and the driven pulley 40 remain in contact with eachother even when a switching between the states where the driving pulley30 and the driven pulley 40 are in contact with and out of contact fromeach other is disabled, and thus the impeller 20 rotates in case of afailure of the actuator 50. Accordingly, the coolant water is suppliedto the engine so as to restrict the engine from being overcooled even incase of the failure of the actuator 50.

The actuator 50 is structured in a manner that the slide 51 is pushed bythe resilient force of the spring 54 and is attracted by the negativepressure inside the closed chamber 55, thereby moving the driving pulley30. Thus, the actuator 50 is controlled by utilizing the negativepressure generated by, for example, a suction stroke of a piston of theengine, and thus there is no need to additionally provide a complicatedmechanism including, for example, electrical equipment, a hydraulicmechanism or the like, to the water pump 1.

As shown in FIGS. 5A and 5B, when φA refers to an inner diameter of thedriving pulley 30 and φB refers to an outer diameter of the drivenpulley 40, a pulley ratio of the driving pulley 30 and the driven pulley40 is φA/φB. Here, the inner circumferential surface of the drivingpulley 30 and the outer circumferential surface of the driven pulley 40come out of contact from each other.

In FIG. 5A, when a rotation number N1 refers to the number of rotationsof the driving pulley 30 and a rotation number N2 refers to the numberof rotations of the driven pulley 40, the rotation number N1 is uniquelydetermined on the basis of a speed V of the belt 31 wound around theouter circumference of the driving pulley 30. Between the rotationnumber N2 and the pulley ratio, a relationship of N2=(the pulleyratio)×N1 is established. On the contrary, in FIG. 5B, the outerdiameter of the driven pulley 40 is φB/2 and the pulley ratio is(φA/φB)×2, and thus the rotation number N2 of the driven pulley 40 is(N2×2), that is, the rotation number N2 is doubled compared to when theouter diameter of the driven pulley 40 is φB. When the rotation numberN2 of the driven pulley 40 is doubled, the number of rotations of theimpeller 20 is also doubled because the water pump 1 is configured in amanner that the impeller 20, which is fixedly mounted on the one end ofthe bearing shaft 10, rotates with the driven shaft via the bearingshaft 10.

In FIGS. 5A and 5B, a case in which the number of rotations of theimpeller 20 is increased is explained. However, the number of rotationsof the impeller 20 may be decreased by changing the pulley ratio of thedriving pulley 30 and the driven pulley 40 in a similar manner to thatexplained above.

According to the water pump 1 of this embodiment, the number ofrotations of the impeller 20 is increased and decreased by changing theouter diameter φB of the driven pulley 40, that is, a diameter of thedriven pulley 40. Consequently, the water pump 1 meets a wide range ofrequirements on a discharge volume without changing the impeller 20. Thenumber of rotations of the impeller 20 is also increased and decreasedby changing the inner diameter φA of the driving pulley 30. However, bychanging the outer diameter φB of the driven pulley 40 instead ofchanging the inner diameter φA of the driving pulley 30, the number ofrotations of the impeller 20 is increased and decreased without changinga length of the belt 31. This method is applicable to the water pump 1having different numbers of rotations.

As shown in FIGS. 6A and 6B, when φC refers to the outer diameter of thedriving pulley 30 and φD refers to the outer diameter of the drivenpulley 40, the pulley ratio of the driving pulley 30 and the drivenpulley 40 is φC/φD. A difference from the structure shown in FIGS. 5Aand 5B is that the outer circumferential surface of the driven pulley 40is in contact with the outer circumferential surface of the drivingpulley 30. Other structures shown in FIGS. 6A and 6B are identical tothose shown in FIGS. 5A and 5B.

In FIG. 6A, the rotation number N1 of the driving pulley 30 is uniquelydetermined on the basis of the speed V of the belt 31 wound around theouter circumference of the driving pulley 30 in a similar manner to thatof FIG. 5A. The rotation number N2 of the driven pulley 40 is determinedon the basis of the pulley ratio (φC/φD). Between the rotation number N2and the pulley ratio, a relationship of N2=(the pulley ratio)×N1 isestablished. On the contrary, in FIG. 6B, the outer diameter of thedriven pulley 40 is φD/2 and the pulley ratio is (φC/φD)×2, and thus therotation number N2 is doubled compared to when the outer diameter of thedriven pulley 40 is φD.

According to the water pump 1 shown in FIGS. 6A and 6B, the number ofrotations of the impeller 20 may be increased and decreased by changingthe outer diameter φD of the driven pulley 40. When the rotation numberN2 of the driven pulley 40 is doubled, the number of rotations of theimpeller 20 is also doubled because the water pump 1 is configured in amanner that the impeller 20, which is fixedly mounted on the one end ofthe bearing shaft 10, rotates with the driven shaft via the bearingshaft 10.

According to the water pump 1 having the structure shown in FIGS. 6A and6B, the number of rotations of the impeller 20 is increased anddecreased by changing the outer diameter φB of the driven pulley 40,that is, by changing the pulley ratio. Consequently, the water pump 1meets a wide range of requirements on the discharge volume withoutchanging the impeller 20. The number of rotations of the impeller 20 isalso increased and decreased by changing the outer diameter φC of thedriving pulley 30, that is, by changing a diameter of the driving pulley30. This is effective in case there is a space constraint at the insideof the driving pulley 30.

As shown in FIG. 7, a water pump 1 a (the fluid pump) related to asecond embodiment of this disclosure includes a driven pulley 40 a (thedriven wheel) and a bearing shaft 10 a (the drive shaft) each having adifferent shape from those of the water pump 1 shown in FIG. 1. Thewater pump 1 a also includes an overall length L1 that is less than thatof the water pump 1. Other structures are identical to those of thewater pump 1. In the second embodiment, the identical numericaldesignations are given to the functions and the structures that areidentical to those of the first embodiment. Differences in the structurebetween the water pump 1 and the water pump 1 a will be explainedhereunder.

The driven pulley 40 a and the bearing shaft 10 a both included in thewater pump 1 a are manufactured integrally with each other by pressworking. A pump body 11 a (the housing) is provided in a manner that apart of the pump body 11 a is positioned at an inside of the drivenpulley 40 a. A bearing 13 a is provided between the pump body 11 a andthe driven pulley 40 a in a radial direction of the driven pulley 40 a.The bearing 13 a supports the driven pulley 40 a that is formedintegrally with the bearing shaft 10 a. Other structures and anoperation of the water pump 1 a are identical to those of the water pump1.

The water pump 1 a, which provides identical effects obtained from thewater pump 1 shown in FIG. 1, has a higher mountability on a vehiclecompared to the water pump 1 because the pump body 11 a is provided in amanner that a part of the pump body 11 a is positioned at an inside ofthe driven pulley 40 a, and thus the overall length L1 of the water pump1 a is less than that of the water pump 1. The water pump 1 a also has ahigher processability because the bearing shaft 10 may be made by pressworking.

As shown in FIG. 8, a water pump 1 b (the fluid pump) of a thirdembodiment of this disclosure is different from the water pump 1 shownin FIG. 1 in that the water pump 1 b has the overall length L1 which isless than that of the water pump 1. Other structures are identical tothose of the water pump 1 shown in FIG. 1. In the third embodiment, theidentical numerical designations are given to the functions and thestructures that are identical to those of the first embodiment.

A driven pulley 40 b (the driven wheel) and a bearing shaft 10 b (thedrive shaft) both included in the water pump 1 b are provided separatelyfrom each other as two parts. A pump body 11 b (the housing) is providedin a manner that a part of the pump body 11 b is positioned at an insideof the driven pulley 40 b. A bearing 13 b is provided between the pumpbody 11 b and the driven pulley 40 b in a radial direction of thebearing 13 b. The bearing 13 b supports the driven pulley 40 b in amanner that the driven pulley 40 b is rotatable unitarily with thebearing shaft 10 b. Other structures and an operation of the water pump1 b are identical to those of the water pump 1.

The water pump 1 b, which provides the identical effects obtained fromthe water pump 1 shown in FIG. 1, has a higher mountability on thevehicle compared to the water pump 1 because the pump body 11 b isprovided in a manner that a part of the pump body 11 b is positioned atan inside of the driven pulley 40 b, and thus the overall length L1 ofthe water pump 1 b is less than that of the water pump 1. In addition,the water pump 1 b also has a higher assemblability or assemblyperformance because the driven pulley 40 b and the bearing shaft 10 bare provided separately from each other as two parts and therefore, thepump body 11 b, the bearing 13 b and the mechanical seal 14 may beassembled on the bearing shaft 10 b from a direction of the actuator 50.

As shown in FIG. 9, a water pump 1 c (the fluid pump) related to afourth embodiment of this disclosure includes a driven pulley 40 c (thedriven wheel) and a bearing shaft 10 c (the drive shaft) each having adifferent shape from those of the water pump 1 shown in FIG. 1. Thewater pump 1 c also includes the overall length L1 that is less thanthat of the water pump 1. In the water pump 1 c, a driving pulleybearing 53 c supporting a driving pulley 30 c (the driving wheel) ismoved in an axial direction of the driving pulley bearing 53 c so that adistance L2 between the pulley bearing 53 c and a belt center 34, thatis, the center of the belt 31 in a belt width direction, is reduced.Other structures are identical to those of the water pump 1 shown inFIG. 1. In the fourth embodiment, the identical numerical designationsare given to the functions and the structures that are identical tothose of the first embodiment.

The driven pulley 40 c and the bearing shaft 10 c both included in thewater pump 1 c are manufactured integrally with each other by pressworking. A pump body 11 c (the housing) is provided in a manner that apart of the pump body 11 c is positioned at an inside of the drivenpulley 40 c. A bearing 13 c is provided between the pump body 11 c andthe driven pulley 40 c in a radial direction of the bearing 13 c. Thebearing 13 c supports the driven pulley 40 c in a manner that the drivenpulley 40 c is rotatable unitarily with the bearing shaft 10 c. Thedriving pulley 30 c is supported by a driving pulley bearing shaft 32 cvia the bearing 53 c in a manner that the driving pulley 30 c rotatesunitarily with the driving pulley bearing shaft 32. The bearing 53 c ispositioned between an actuator 50 c (the displacement mechanism) and thebelt center 34 c in an axial direction of the bearing 53 c. A slide 51 cis provided at one end of the bearing shaft 10 c which is closer to theactuator 50 c. The slide 51 c is movable in the perpendicular direction62 relative to the direction of the resultant force 61 caused by thebelt 31 that is wound around the outer circumferential surface of thedriving pulley 30 c. Other structures are identical to those of thewater pump 1 shown in FIG. 1.

The water pump 1 c, which provides the identical effects obtained fromthe water pump 1 shown in FIG. 1, has a higher mountability on thevehicle compared to the water pump 1 because the pump body 11 c isprovided in a manner that a part of the pump body 11 c is positioned atan inside of the driven pulley 40 c, and thus the overall length L1 ofthe water pump 1 c is less than that of the water pump 1. In addition,the distance L2 between the pulley bearing 63 c and the belt center 34may be reduced. The driving pulley bearing 53 c receives a bending load(the resultant force 61×the distance L2) caused by the resultant force61 caused by the belt 31, however, the bending load is reduced byreducing the distance L2. Thus, in case that the bending load applied tothe driving pulley bearing 53 c is reduced, an unbalanced load appliedto the driving pulley bearing 53 c is reduced, resulting in a longerlife of the driving pulley bearing 53 c.

According to the first, second, third and the fourth embodiments of thisdisclosure, the power from the engine is transmitted from the drivingpulley 30, 30 c to the driven pulley 40, 40 a, 40 b, 40 c by means ofthe friction force generated between the driving pulley 30, 30 c and thedriven pulley 40, 40 a, 40 b, 40 c. However, the power from the enginemay be transmitted by means of an engagement of gears. In this case, agear ratio is used instead of the pulley ratio between the drivingpulley 30, 30 c and the driven pulley 40, 40 a, 40 b, 40.

The embodiments of this disclosure are not limited to the water pump 1,1 a, 1 b, 1 c but may apply, for example, to an oil pump.

The pressure in the closed chamber 55 that controls the actuator 50, 50c may be controlled by applying a positive pressure instead of thenegative pressure.

In order to cause the driving pulley 30, 30 c to come in contact withthe driven pulley 40, 40 a, 40 b, 40 c, a resilient body including butnot limited to a rubber or air spring may be used instead of the spring.

According to the embodiments, the water pump 1, 1 a, 1 b, 1 c includesthe bearing shaft 10, 10 a, 10 b, 10 c driven by the power from theengine, the impeller 20 adapted to be provided at the pump body 11, 11a, 11 b and at the engine block 12 and rotating unitarily with thebearing shaft 10, 10 a, 10 b, 10 c, the driving pulley 30, 30 c which isprovided separately from the bearing shaft 10, 10 a, 10 b, 10 c and towhich the power from the engine is always transmitted when the engine isrunning, the driven pulley 40, 40 a, 40 b, 40 c transmitting the powerfrom the engine to the bearing shaft 10, 10 a, 10 b, 10 c upon being incontact with the driving pulley 30, 30 c, and the actuator 50, 50 ccausing the driving pulley 30, 30 c and the driven pulley 40, 40 a, 40b, 40 c to be out of contact from each other by moving at least one ofthe driving pulley 30, 30 c and the driven pulley 40, 40 a, 40 b, 40 c.

Due to the above described structure, the actuator 50, 50 c causes thedriving pulley 30, 30 c and the driven pulley 40, 40 a, 40 b, 40 c to beout of contact from each other. Consequently, when the engine starts up,the impeller 20 is stopped rotating, and thus the overcooling of theengine is restricted and the warm-up time of the engine is reduced. Inaddition, no power from the engine is transmitted to the impeller 20,thereby restricting the wasted consumption of the power.

According to the embodiments, the power from the engine is transmittedto the driving pulley 30, 30 c by means of the belt 31 and the actuator50, 50 c moves the driving pulley 30, 30 c in the perpendiculardirection 62 perpendicular to the direction of the resultant force 61 ofthe tensile force 60 a and the tensile force 60 b that act on thedriving pulley 30, 30 c.

Due to the above described structure, the actuator 50, 50 c moves thedriving pulley 30, 30 c in the perpendicular direction 62 perpendicularto the direction of the resultant force 61 of the tensile force 60 a andthe tensile force 60 b both acting on the driving pulley 30, 30 c. Thus,the resultant force 61 of the pressing forces that are caused by thebelt 31 and are applied to the actuator 50, 50 c is less likely tointerfere with the movement of the actuator 50. Thus, the force of theactuator 50 for moving the driving pulley 30, 30 c is restricted fromacting against the resultant force 61 of the pressing forces that arecaused by the belt 31 and are applied to the actuator 50, 50 c.Consequently, the actuator 50, 50 c needs to supply only sufficientforce to move the driving pulley 30, 30 c, and as a result, the actuator50, 50 c having a small size is provided.

According to the embodiments, the driving pulley 30, 30 c has acylindrical shape which includes the hollow portion and the drivenpulley 40, 40 a, 40 b, 40 c is provided at an inside of the hollowportion of the driving pulley 30, 30 c.

Due to the above described structure, the driven pulley 40, 40 a, 40 b,40 c is provided at the inside of the driving pulley 30, 30 c. Thus, thedriving pulley 30, 30 c and the driven pulley 40, 40 a, 40 b, 40 c arearranged so as to overlap each other in the radial direction of thebearing shaft 10, 10 a, 10 b, 10 c. As a result, the size of the waterpump 1, 1 a, 1 b, 1 c is reduced in the axial direction of the bearingshaft 10, 10 a, 10 b, 10 c.

According to the embodiments, the driving pulley 30, 30 c and the drivenpulley 40 a, 40 b, 40 c are configured to be unitarily rotatable witheach other and the bearing 13 a, 13 b, 13 c is provided between theinner circumferential surface of the driven pulley 40 a, 40 b, 40 c andthe pump body 11 a, 11 b, 11 c in the radial direction of the drivenpulley 40 a, 40 b, 40 c.

Due to the above described structure, the bearing 13 a, 13 b, 13 c isprovided between the inner circumferential surface of the driven pulley40 a, 40 b, 40 c and the pump body 11 a, 11 b, 11 c in the radialdirection of the driven pulley 40 a, 40 b, 40 c. Thus, the drivingpulley 30, 30 c and the driven pulley 40 a, 40 b, 40 c are arranged soas to overlap each other in the radial direction of the bearing shaft 10a, 10 b, 10 c. As a result, the size of the water pump 1 a, 1 b, 1 c isreduced in the radial direction of the bearing shaft 10 a, 10 b, 10 c.

According to the embodiments, the actuator 50, 50 c includes the spring54 for causing the driving pulley 30, 30 c to be in contact with thedriven pulley 40, 40 a, 40 b, 40 c by means of the resilient force.

Due to the above described structure, the actuator 50, 50 c includes thespring 54 for causing the driving pulley 30, 30 c to be in contact withthe driven pulley 40, 40 a, 40 b, 40 c by means of the resilient force.Thus, the driving pulley 30, 30 c and the driven pulley 40, 40 a, 40 b,40 c are in contact with each other by means of the resilient force ofthe spring 54 when the actuator 50, 50 c is under no control, that is,the pressure in the actuator 50, 50 c is under no control, therebyoperating the water pump 1, 1 a, 1 b, 1 c. Consequently, the drivingpulley 30, 30 c and the driven pulley 40, 40 a, 40 b, 40 c remain incontact with each other even in case that the actuator 50, 50 c fails,thereby operating the water pump 1, 1 a, 1 b, 1 c, which provides thefail-safe structure.

According to the embodiments, the actuator 50, 50 c moves the drivingpulley 30, 30 c by means of the resilient force of the spring 54 and bymeans of the gas pressure.

Due to the above described structure, the actuator 50, 50 c moves thedriving pulley 30, 30 c by means of the resilient force of the spring 54and the gas pressure. Consequently, the actuator 50, 50 c is controlledby utilizing the pressure existing around the engine, and thus there isno need to additionally provide the complicated mechanism including, forexample, the electrical equipment, the hydraulic mechanism or the like,to the water pump 1, 1 a, 1 b, 1 c.

According to the embodiments, the number of rotations of the impeller 20is determined on the basis of the ratio of the diameter of the drivingpulley 30, 30 c and the diameter of the driven pulley 40, 40 a, 40 b, 40c.

Due to the above described structure, the number of rotations of theimpeller 20 is determined on the basis of the ratio of the diameter ofthe driving pulley 30, 30 c and the diameter of the driven pulley 40, 40a, 40 b, 40 c. Consequently, the discharge volume of the water pump 1, 1a, 1 b, 1 c is set at the desired value simply by changing the drivingpulley 30, 30 c or the driven pulley 40, 40 a, 40 b, 40 c. As a result,without changing the impeller 20, the water pump 1, 1 a, 1 b, 1 c thatmeets a wide range of the requirements on the discharge volume isprovided.

The principles, preferred embodiments and mode of operation of thepresent invention have been described in the foregoing specification.However, the invention which is intended to be protected is not to beconstrued as limited to the particular embodiments disclosed. Further,the embodiments described herein are to be regarded as illustrativerather than restrictive. Variations and changes may be made by others,and equivalents employed, without departing from the spirit of thepresent invention. Accordingly, it is expressly intended that all suchvariations, changes and equivalents which fall within the spirit andscope of the present invention as defined in the claims, be embracedthereby.

The invention claimed is:
 1. A fluid pump, comprising: a drive shaftdriven by power from an engine; a rotor adapted to be provided at ahousing and rotating unitarily with the drive shaft; a driving wheelwhich is provided separately from the drive shaft, to which the powerfrom the engine is always transmitted when the engine is running, and towhich the power from the engine is directly transmitted via a powertransmitting member; a driven wheel transmitting the power from theengine to the drive shaft upon being in contact with the driving wheel;and a displacement mechanism causing the driving wheel and the drivenwheel to be out of contact from each other by moving the driving wheel.2. The fluid pump according to claim 1, wherein the displacementmechanism moves the driving wheel in a perpendicular direction to adirection of a resultant force of forces that act on the driving wheel.3. The fluid pump according to claim 1, wherein the driving wheel has acylindrical shape which includes a hollow portion and the driven wheelis provided at an inside of the hollow portion of the driving wheel. 4.The fluid pump according to claim 2, wherein the driving wheel has acylindrical shape which includes a hollow portion and the driven wheelis provided at an inside of the hollow portion of the driving wheel. 5.The fluid pump according to claim 1, wherein the driving wheel and thedriven wheel are configured to be unitarily rotatable with each otherand a bearing is provided between an inner circumferential surface ofthe driven wheel and the housing in a radial direction of the drivenwheel.
 6. The fluid pump according to claim 2, wherein the driving wheeland the driven wheel are configured to be unitarily rotatable with eachother and a bearing is provided between an inner circumferential surfaceof the driven wheel and the housing in a radial direction of the drivenwheel.
 7. The fluid pump according to claim 3, wherein the driving wheeland the driven wheel are configured to be unitarily rotatable with eachother and a bearing is provided between an inner circumferential surfaceof the driven wheel and the housing in a radial direction of the drivenwheel.
 8. The fluid pump according to claim 1, wherein the displacementmechanism includes a resilient member for causing the driving wheel tobe in contact with the driven wheel by means of a resilient force. 9.The fluid pump according to claim 2, wherein the displacement mechanismincludes a resilient member for causing the driving wheel to be incontact with the driven wheel by means of a resilient force.
 10. Thefluid pump according to claim 3, wherein the displacement mechanismincludes a resilient member for causing the driving wheel to be incontact with the driven wheel by means of a resilient force.
 11. Thefluid pump according to claim 5, wherein the displacement mechanismincludes a resilient member for causing the driving wheel to be incontact with the driven wheel by means of a resilient force.
 12. Thefluid pump according to claim 8, wherein the displacement mechanismmoves the driving wheel by means of the resilient force of the resilientmember and by means of a gas pressure.
 13. The fluid pump according toclaim 9, wherein the displacement mechanism moves the driving wheel bymeans of the resilient force of the resilient member and by means of agas pressure.
 14. The fluid pump according to claim 10, wherein thedisplacement mechanism moves the driving wheel by means of the resilientforce of the resilient member and by means of a gas pressure.
 15. Thefluid pump according to claim 11, wherein the displacement mechanismmoves the driving wheel by means of the resilient force of the resilientmember and by means of a gas pressure.
 16. The fluid pump according toclaim 1, wherein a number of rotations of the rotor is determined on thebasis of a ratio of a diameter of the driving wheel and a diameter ofthe driven wheel.
 17. The fluid pump according to claim 2, wherein anumber of rotations of the rotor is determined on the basis of a ratioof a diameter of the driving wheel and a diameter of the driven wheel.18. The fluid pump according to claim 3, wherein a number of rotationsof the rotor is determined on the basis of a ratio of a diameter of thedriving wheel and a diameter of the driven wheel.
 19. The fluid pumpaccording to claim 5, wherein a number of rotations of the rotor isdetermined on the basis of a ratio of a diameter of the driving wheeland a diameter of the driven wheel.
 20. The fluid pump according toclaim 8, wherein a number of rotations of the rotor is determined on thebasis of a ratio of a diameter of the driving wheel and a diameter ofthe driven wheel.
 21. The fluid pump according to claim 1, wherein thedisplacement mechanism is a radial displacement mechanism.